1. Field of the Invention
The present invention relates to a throttle valve capable of changing the amount of intake air into an engine.
2. Description of the Related Art
In a conventional throttle valve, as shown in FIG. 23, an air eddy of turbulent airflow which occurs downstream of a valve body is controlled to become small, so that airflow noises are suppressed, by two or more straightening vanes which straighten the intake air on the downstream side surface of the valve body. These straightening vanes are fan-shaped in a cross sectional view and disposed in parallel at an equal interval in a rotational axis extending direction, wherein the vanes are disposed on the valve body so as to be perpendicular to the rotational axis. For a further description of the straightening vanes, refer to, for example, Japanese Laid Open Patent No. 2000-204975.
However, in the above-mentioned conventional technology, these straightening vanes serve as airflow resistance to the intake air, which is a factor of lowering the maximum output of the engine and of worsening the gas mileage.